The present invention relates to processes for the modification of recorded data and, more particularly, to a novel method for the direct over-write modification of digital data stored in domains of a magneto-optical recording media.
It is known to store each binary bit of information in a digital data stream in one associated one of a sequential multiplicity of domains formed in magnetic storage media. While many different types of magnetic media have been hitherto used, including plated wires, toroidal cores, tapes and the like, the particular high-information-density media of interest here is a thin film layer of a magneto-optic recording material, such as amorphous alloys of terbium cobalt (TbCo), gadolinium terbium cobalt (GdTbCo), and the like materials, which alloys allow the binary value of a stored bit of information to be determined by analyzing the effect of each data storage region upon a light beam reflected from the surface of that recording layer region. It is known that, because these ferrimagnetic materials are chosen to have a high coercivity at room temperatures and low coercivity at higher temperatures, heating of a small region of any of these materials can be "written" to have a net magnetization which is not only substantially perpendicular to the surface of the film but is also established in that direction parallel to the direction in which an external (bias) magnetic field was directed at the time when that particular region was heated and allowed to subsequently cool. It is also well known to change the external field direction to encode the data to be stored, and to change the previously stored information by re-heating the film region while an external bias magnetic field is presented in the desired (opposite) direction through the region. However, the speed at which the external field can be made to reverse cannot presently be made as fast as is desired; this form of storage media, while having demonstrated both (1) sufficient data density for the storage of gigabits of information on each disk and (2) short time for access to the previously stored data, has not hitherto allowed the stored data to be modified at any speed even close to the speed at which stored data can be read from the storage disk. For general use, data storage equipment should be capable of writing, reading and/or over-writing data at the same high rate. Accordingly, it is highly desirable to provide a method by which to rapidly modify the data stored in at least one selected one of a multiplicity of microscopic recording regions of a magneto-optical recording medium.